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We present evidence for an anti-correlation between faint QSOs and B < 23 galaxies.A sample of 192 QSOs in a 2.5 deg2 area has been imaged using the Isaac Newton Telescope Wide-Field Camera. The cross-correlation signal is of a similar amplitude to the galaxy auto-correlation function at the limit of B < 23, but is negative in sign. As fainter galaxies are selected the negative correlation signal becomes less significant, until the signal is effectively zero at B < 26. We propose two alternate explanations for the observed effect. The first is gravitational lensing of the faint background QSOs, which have a flat number count slope. However, the lensing signal is significantly higher than expected in conventional models. The second possibility is that inter-galactic dust absorption is responsible. A reddening of only E(B - V) ≃ 0.02 is required to produce the observed correlation. The large 2dF and SDSS QSO surveys should allow a definitive solution to the question of QSO–galaxy correlations.

Presolar grains in meteorites formed in a sample of Asymptotic Giant Branch (AGB) stars that ended their lives within ≈1 Gyr of the origin of the Solar System 4.6 Gyr ago. The O-isotopic compositions of presolar O-rich stardust reflect the masses and metallicities of their parent stars. We present simple Monte Carlo simulations of the parent AGB stars of presolar grains. Comparison of model predictions with the grain data allow some broad conclusions to be drawn: (1) Presolar O-rich grains formed in AGB stars of mass ∼1.15–2.2 M⊙. The upper-mass cutoff reflects dredge-up of C in more massive AGB stars, leading to C-rich dust rather than O-rich, but the lack of grains from intermediate-mass AGB stars (>4 M⊙) is a major puzzle; (2) The grain O-isotopic data are reproduced well if the Galaxy in presolar times was assumed to have a moderate age-metallicity relationship, but with significant metallicity scatter for stars born at the same time; (3) The Sun appears to have a moderately low metallicity for its age and/or unusual 17O/16O and 18O/16O ratios for its metallicity; and (4) The Solar 17O/18O ratio, while unusual relative to present-day molecular clouds and protostars, was not atypical for the presolar disk and does not require self-pollution of the protosolar molecular cloud by supernova ejecta.

The oxygen isotopic compositions of densely packed submicron oxide grains in two grain separates of different grain size from the CM2 carbonaceous chondrite Murray were determined by multi-detection raster imaging on the NanoSIMS ion microprobe. This led to the identification of 81 presolar spinel and 3 presolar corundum grains among ∼51 700 grains in the CF residue (mean diameter 0.15 µm) and 171 presolar spinel and 29 presolar corundum grains among ˜21 500 grains in the CG residue (mean diameter 0.45 µm). Previous NanoSIMS analysis of individual grains from the same residues has led to the discovery of 15 presolar spinel and 3 presolar corundum grains among 628 CF grains, and 9 presolar spinels among 753 CG grains. The oxygen isotopic compositions of the presolar oxides found by raster imaging are comparable to those of the presolar oxides measured individually. While the abundance of presolar spinel among the (larger) grains of the CG residue is the same for both techniques, the detection efficiency for presolar spinel by imaging among the (smaller) grains in CF is lower due to the small size of these grains. Nonetheless, it is possible to identify presolar grains of this size range. Though single grain measurements are effective for determining the precise isotopic compositions and abundances of presolar grains, raster ion imaging is the method of choice in searches for rare presolar grain types such as presolar silicates.

We studied the dynamic influence of a dust component on the gaseous phase in central regions of galactic disks. We performed two-dimensional hydrodynamic simulations for flat, multicomponent disks embedded in a stellar and dark matter potential. The pressure-free dust component is coupled to the gas by a drag force depending on their velocity difference. The most unstable regions are those with either a low or near-to-minimum Toomre parameter or with rigid rotation, i.e. the central area. In those regions the dust-free disks become most unstable for a small range of high azimuthal modes (m ∼ 8), whereas in dusty disks all modes have similar amplitudes resulting in a patchy appearance. The structures in the dust have a larger contrast between arm and interarm regions than those of the gas. The dust peaks are frequently correlated with peaks of the gas distribution, but they do not necessarily coincide with them. This leads to a large scatter in the dust to gas ratios. The appearance of the dust is more cellular (i.e. sometimes connecting different spiral features), whereas the gas is organised in a multi-armed spiral structure. We found that an admixture of 2% dust (relative to the mass of the gas) destabilises gaseous disks substantially, whereas dust to gas ratios below 1% have no influence on the evolution of the gaseous disk. For a high dust to gas ratio of 10% the instabilities reach the saturation level after 30 Myr.

In this paper we present a new method for obtaining the optical wavelength-dependent reddening function of planetary nebulae (PN), using the nebular and stellar continuum. The data used was a spectrum of NGC 6302 obtained using the Double Beam Spectrograph on the 2.3 m telescope at Siding Springs Observatory over three nights. This resulted in a spectrum covering a wavelength range 3300–8600 Å with a large dynamical range and a mean signal to noise of >102 Å−1 in the nebular continuum. With such a high S/N the continuum can be accurately compared with a theoretical model of nebular plus stellar continuum. The nebular electron temperature and density used in the model are determined using ratios of prominent emission lines. The reddening function can then be obtained from the ratio of the theoretical and the observed continuum. In the case of NGC 6302, it is known that much of the reddening arises from dust within or around the nebula, so that any differences between the measured reddening law and the 'standard' interstellar reddening law will reflect differences in the nebular grain size distribution or composition. We find that for NGC 6302, the visible to IR extinction law is indistinguishable from 'standard' interstellar reddening, but that the UV extinction curve is much steeper than normal, suggesting that more small dust grains had been ejected into the nebula by the PN central star. We have detected the continuum from the central star and determined its Zanstra temperature to be of order 150,000 K. Finally, using the extinction law that we have determined, we present a complete dereddened line list of nearly 600 emission lines, and report on the detection of the He(2–10) and He(2–8) Raman features at λ4331 Å and λ4852 Å, and the detection of Raman scattered O VI features at λ6830 Å and λ7087 Å. We believe this to be the first detection of this process in a PN.

Primitive meteorites and interplanetary dust particles contain small grains that originated in stellar outflows and supernova explosions. These μm- and sub-μm-sized presolar grains can be isolated and studied for their isotopic compositions in the laboratory. They are recognised as stardust by their isotopic compositions, which are completely different from those of the Solar System. They provide new information on stellar evolution, nucleosynthesis, mixing processes in asymptotic giant branch (AGB) stars and supernovae, and Galactic chemical evolution. Red giants, AGB stars, Type II supernovae and possibly novae have been identified as stellar sources of the grains. Of the eight nuclear processes proposed by Burbidge et al. (1957), signatures of all except the r-process can be found in presolar dust grains.

Primitive meteorites contain small amounts of presolar minerals that formed in the winds of evolved stars or in the ejecta of stellar explosions. Silicon carbide is the best studied presolar mineral. Based on its isotopic compositions it was divided into distinct populations that have different origins: Most abundant are the mainstream grains which are believed to come from 1.5–3 M⊙ AGB stars of roughly solar metallicity. The rare Y and Z grains are likely to come from 1.5–3 M⊙ AGB stars as well, but with subsolar metallicities (0.3–0.5 times solar). Here we report on C and Si isotope and trace element (Zr, Ba) studies of individual, submicrometer-sized SiC grains. The most striking results are: (1) Zr and Ba concentrations are higher in Y and Z grains than in mainstream grains, with enrichments relative to Si and solar of up to 70 times (Zr) and 170 times (Ba), respectively; (2) For the Y and Z grains there is a positive correlation between Ba concentrations and amount of s-process Si. This correlation is well explained by predictions for 2–3 M⊙ AGB stars with metallicities of 0.3–0.5 times solar. This confirms low-metallicity stars as most likely stellar sources for the Y and Z grains.

Astronomical light echoes, the time-dependent light scattered by dust in the vicinity of varying objects, have been recognized for over a century. Initially, their utility was thought to be confined to mapping out the three-dimensional distribution of interstellar dust. Recently, the discovery of spectroscopically useful light echoes around centuries-old supernovae in the Milky Way and the Large Magellanic Cloud has opened up new scientific opportunities to exploit light echoes.

In this review, we describe the history of light echoes in the local Universe and cover the many new developments in both the observation of light echoes and the interpretation of the light scattered from them. Among other benefits, we highlight our new ability to classify outbursting objects spectroscopically, view them from multiple perspectives, obtain a spectroscopic time series of the outburst, and establish accurate distances to the source event. We also describe the broader range of variable objects with properties that may be better understood from light-echo observations. Finally, we discuss the prospects of new light-echo techniques not yet realized in practice.

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